Hello.
I deleted a chunk of track that I happened to be sitting on in my motocar, and received this error!
'tis a great mod though, I use it extensively for my railway megabase.

The mod Railway Motor Car (0.2.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event railway-motor-car::on_nth_tick(30)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__railway-motor-car/scripts/use_equipment.lua:184: in function <railway-motor-car/scripts/use_equipment.lua:150>

Update, it seems to be bot deconstruction of the motorcar itself.
If I delete just the tracks, the bots patiently wait until I get out.

Thanks for the report.
I disabled the deconstruction with version 0.2.2